Replenishable fire detector



Dec. 15, 1964 IN VENTOR. JOHN E. L/NDBERG, J/a.

BY M

AT 1' ORJYE'Y United States Patent 3,161,865 REPLENISHABLE FIRE DETECTOR John E. Lindberg, Jr., 1170 Oleander Drive, Lafayette, Calif.

Original application May 25, 1959, Ser. No. 815,406, new Patent No. 3,122,728, dated Feb. 25, 1964. Divided and this application Nov. 17, 1960, Ser. No. 70,030

8 Claims. (Cl. 340-429) This invention relates to improvements in method and apparatus for heat detection and especially fire detection. This application is a division of application Serial Number 815,406, filed May 25, 1959, now Patent No. 3,122,- 728.

The invention is characterized by its provision of a novel non-electric heat-detecting element or sensor able to detect at any selected critical temperature over a wide range. Only the detecting sensor is located in a fire Zone (or other heat-detection zone), and it is connected, preferably outside the zone, to an electrical warning or corrective system by a novel instrument that I term a responder. The responder may most conveniently be located outside the zone in which detection is desired, though usually close to it. The actual alarm or heat-condition indicator can be connected to the responder by a wire of practically any desired length. For example, the non-electric heat-detecting sensor may be inside a house, the responder just outside the house, and the! indicator at the fire station. Or, the non-electric heat-detecting sensor may be in zone 1 of an aircraft engine, ahead of a fire Wall; then the responder may be behind the fire wall, and the indicator on the aircraft instrument panel. Furthermore, the novel heat-detecting sensor may be filamen-tary-a long, very-narrow-diameter, hollow tube, which may extend along a line, around a circle, or along any desired path and for practically any desired length.

The advantages of the invention in home fire detection and the like are apparent. Less apparent may be the use of the invention in regions inaccessible to direct observation. Examples of such regions include: the interiors of engine nacelles of aricraft and remotely located installations of power-generating equipment. The invention is also useful for detecting fire or overheat conditions at any point in any vehicle or building, and also has numerous commercial and industrial applications.

An important object of the invention is to providea fire-detection system for use in aircraft in zone 1, ahead of the fire wall of the power plant (i.e., the region in an engine nacelle ahead of the fire Wall).

Conventional fire detectors employed in aircraft for zone-1 fire detection, whether of the continuous type or of the single-point type, have relied upon electrical'circuits that extend into the fire zone. For example, a prevailing type of continuous fire detector is actuated by the change in electrical resistance of semi-conducting materials caused by a change in environmental temperature. The trouble is that false alarms have plagued all heat and fire-detecting systems that rely. on electrical circuits extending into the fire zone. For example, the moisture conditions in the engine chambers, where zone-l detectors are located, vary considerably, because changes in altitude radically affect the temperature and pressure conditions there. As a consequence, moisture condensation occurs frequently and has often caused electrical fire detectors to develop low-resistance shorts that resulted in false alarms.

False alarms are serious enough on the'ground, as

everyone knows, but in aircraft they are Unforgivable, be-

cause the crew must immediately take hazardous and ex pensive emergency action. The present inven'tion'solves the problem of preventing moisture, and other atmospheric conditions from causing false alarms, and it does this by operating without needing any electrical circuit in the fire zone, by using a sensor that is never actuated by moisture or by atmospheric conditions, and by using a low-impedance circuit outside the fire zone.

This invention also eliminates other factors that led to false alarms or failures in prior-art devices. Such problems as poor electrical connections at the joints between successive elements of continuous-type detectors, and the accumulation of foreign material in the connections, both leading to trouble, cannot occur in this invention. My invention uses only the simplest electrical connection and normally locates that connection at or behind the fire wall, where it is well protected.

An outstanding feature of the invention is that the warning circuit can be operated at an impedance of less than one ohm. This feature greatly increases the reliability of the system, for this impedance is so low that complete immersion of the circuit in water does not seriously aifect its operation.

Some prior-art types of fire detectors have given false alarms because they responded to the rate of change of temperature rather than, or in addition to, a predetermined high temperature level. Consequently, during airplane takeotf, when the temperature in the power-plant area increases very rapidly, these detectors sometimes gave false alarms when everything was normal. The same thing happened during rapid climbing and some other operating conditions. The device of this invention is not affected by the rate of change of temperature; so another source of false alarms is obviated.

Prior-art continuous-type fire detectors also gave false alarms whenever the detector element was seriously damaged, because short circuit were then caused within the element. The sensor of the present invention can be completely severed, cut open, dented, or bent in any fashion without causing a false alarm.

Another object of the invention is to provide a fire detector substantially lighter in weight-per-length than previous fire detectors, an important feature because every pound saved in equipment means that additional payload is available. In modern transport aircraft, each pound saved in manufacture is considered to be worth about $60 to $100. The fire detector of the present invention weighs only about one-seventh as much as the lightest comparable prior-art detectors.

Another object is to provide a fire-detection system which avoids the complexities characteristic of the circuits and mechanical elements of other fire. detectors. For example, no amplifiers or relays are used in this system.

An additional object is to provide a non-sealed system capable of repeated use in fire detection for a large nurn ber of times. A further object is to provide a novel test system for the fire detection system.

Other objects and advantages of the invention will ap- B and containing means E responsive toheat in the environment of the sensor A, for raising the pressure in the responder B. The responder B may be thought of as a pressure-actuated electrical switch that opens or closes the electrical circuit C in response topr'essure changes induced by the sensor A as it responds to heat. The

electrical circuit C may be a warning circuit or a'remedial V circuit. Several responders B may be used in one circuit,

Patented Dec. 15, 1964 are useful in this invention.

' forms pseudo-hydrides.

if desired, to control it in some manner that depends on r the temperature conditions of the environments to which the sensors A are exposed.

The sensor A preferably comprises a narrow-diameter metal tube D of constant cross-sectional area and of any desired length. Within this enclosure D is means E responsive to the temperature of the enclosure D for varying; the pressure inside the enclosure D. This means B may also be referred to as a transducing agent or as a gas-releasing agent. The enclosure D is gas-tight and its only opening is connected to the responder B, which itself defines a closed chamber connected to the enclosure D. An alteration of the internal pressure within the enclosure D therefore affects the responder B.

'Severa'l basic types of materials are suitable transducing agents E: (1) materials that do not liberate gas until a triggering temperature is reached and then liberate it sharply and quickly; (2) materials that retain gas at low temperatures and liberate gas progressively over a wide range of elevated temperatures; and (3) materals that retain relatively small quantities of gas at low temperatures and absorb large quantities of gas as the temperature'is elevated over a wide range.

Typical of category (1) above are the blowing agents,

which have heretofore been used in the manufacture of sponge rubber and foam plastic. Typical blowing agents are:

(a) Celogen, a white crystalline powder with a specific gravity of 1.56 that decomposes at about 151 C. to 156 C., liberating about 105 to 110 cc. of non-condensable gas per gram of powder, 98.45% of the gas being nitrogen. Chemically, it is a p,p' oxy bis (benzene sulfonyl' hydrazide);

(b) Unicel ND, a white powder that decomposes at 180 C. to 190 C, liberating about 116 cc. of gas per 'gram of powder, 90 to 95% of the gas being nitrogen. Chemically, it is dinitrosopentamethylenetetramine.

Class (2) above includes heat-dissociable materials such as the alkaline and alkaline earth hydrides, the hydrides of certain other metals listed below, and some borohydrides. These materials, when subjected to an increase in temperature, liberate gas and therefore may be employedas a-means for altering the internal pressure of a container D in which they are enclosed. With the alkali and alkaline earth metals, i.'e., groups I-a and' II-a of the periodic table, hydrogen forms stoichiometric compounds such as sodium hydride and calcium hydride. These are ionic in behaviour, with hydrogen as the negative ion. The reactions are reversible and exothermic and Specifically, hydrogen reacts with lithium, sodium, potassium, rubidium, cesium,

,c alcium, radium, strontium, francium, and barium, in

stoichiometric proportions to form hydrides.

v Hydrogen reacts with aluminum to form aluminum hydride and complex alumino hydrides such as lithium alumino hydride, magnesium alumino hydride, and sodium 'alumino hydride.

With the elements of Groups Ilka (including the rare earth and actinide elements), IV-a, and Va, hydrogen The solubility of hydrogen in elements of these groups varies as the square root of the pressure, and it decreases withincrease in temperature. Elements of these groups are designated as Group B,

the class consisting of scandium, titanium, vanadium,f

y-tterbiurn, zirconium, niobium, hafnium, tantalum, the rare earth metals (atomic numbers 57 through 71), and

drated chabasite acts similarly with gases such as hydrogen and carbon dioxide.

These are merely examples of class (2) materials as defined above, and do not by any means exhaust the list. However, they do exemplify the materials that retain gas at low temperatures and release gas progressively as the temperature is raised.

Class (3.) materials, in contrast to those of class (2), absorb gas when subjected to a temperature elevation. They also may be employed to alter the internal pressure of a container in which they are enclosed. For example, hydrogen interacts with what are known as the Group A metals, consisting of copper, silver, molybdenum, tungsten, iron, cobalt, nickel, aluminum, platinum, manganese, technetium, rhenium, osmium, iridium, ruthenium, and rhodium; chromium is a member of this group at temperatures greater than about 300 C. The action appears to be a type of solubility, and the solubility increases with increasing temperature. Certain borohydrides also behave in this manner.

Some transducing agents, notably group B hydrides which have become contaminated with oxygen, even though they outgas well when heated, do not re-ingas completely upon subsequent cooling. They are not suitable for use in sealed sensors if a reliable indication of the removal of a fire condition is desired, since the sensor pressure will remain above its initial value even after the fire has gone out. However, there are'some applications in which it is inevitable that the transduci'ng agent will become contaminated with oxygen. For example, the sensor may have to be made up of short, interchangeable sections connected together by gas-tight fittings, and contamination will occur when the sensor sections are changed. The drawing shows a preferred form of device for use in such cases, where the transducing agents do not re-ingas completely.

A sensor A may be filled with a transducing agent E which, for some reason, is not expected to re-ingas properly. The end 2'50 of the sensor A extends through a partition or firewall 251 and is connected through a tube 252 to a bellows 253 and an electrically-operated, normally-closed solenoid valve 254. When the valve 254 is closed, the interiors of the bellows 253, the tube 252, and .the sensor tube D share a common atmosphere to the exclusion of all others. A tube 255 connects the valve 25s to two more valves 256 and 257 like the valve 254. The valve 256 is connected through a pressure regulator 253 to a tank 25h of compressed gas. The valve'257 is vented to the external atmosphere through a short open tube 263.

[are wired in parallel, and their other sides are connected by wires 277 and 2 78 to. one contact 279 of the bellowsoperated switch 263. The other contact 23% of the switch 263 is connected by a wire 28]; to one terminal of a solenoid 282 that controls the valve 256. The other terminal of the solenoid 282 isconnected through a wire 283 to 285 of the switch 273 is connected by a wire 286 to one the 'actinide metals (atomic numbers 89 through 103).;

palladium is a member of this Group Bat temperatures greater than about 300 C. This solution of hydrogen in'afGroup B metal is commonlyte rmed a hydride,

though it is not a stoichiometric compound.

contact 287 of the switch 272, and by a wire 288 to one terminal of ;a solenoid 289 that controls the valve 254.

The other terminal of the soienoid 289 is connected through wires 290 and 264 to the current source 265. The contact 291 of the switch 272 is connectedby a wire 292 to one terminal of a solenoid 293 which controls the .-valve 25?;the other'termina'l'of the solenoid 293 is connected through'wires 294 and 278 to the contact 279 of thes'witch 263.

The switch 263 is actuated by the expansion and contraction of the bellows 253 in response to changes of pressure within the tube 252. The switch 263 is designed, in a Way well known to those skilled in the art of switchmaking, so that it operates by snap-action, that is, When the bellows 253 expands or contracts sufficiently to cause the arm 262 to leave the contact on which it has been resting, the arm 262 immediately snaps over to the other contact. There are therefore only two stable positions for the arm 262--touching either the contact 279 or the contact 280; it cannot remain at an intermediate position.

Operation In normal operation the switches 268 and 271 are open and the valves 254, 256, and 257 are closed. When the sensor A is exposed to a temperature high enough to cause the transducing agent E to outgas, the pressure in the sensor A, the tube 252, and the bellows 253 increases. The pressure increase causes the bellows 253 to expand, and when the bellows 253 expands far enough, the arm 262 of the switch 263 is snapped from the contact 280 to the contact 279. With the arm 262 touching the contact 279, current flows from the source 265 through the wire 264, the arm 262, the contact 279, the wires 278 and 277, the lamp 275, and the bell 276, and returns to the source 265 through the wires 274 and 266. The current lights the lamp 275 and rings the bell 276, giving indication that the temperature of the sensor A has exceeded a certain preselected critical value.

When, however, the temperature of the sensor A drops below the critical value, the transducing agent B may not re-ingas enough to lower the pressure in the bellows 253 sufilciently to snap the arm 262 of the switch 263 back from the contact 279 to the contact 280. In order to determine whether the temperature of the sensor A has dropped below the critical value, it is necessary to close the test switch 272. When the switch 272 is closed (with the arm 262 of the switch 263 still touching the contact 279), current from the source 265flows through the wires 264 and 299 and the solenoid 2S9, causing the valve 254 to open, and then returns to the source 265 through the Wires 288 and 286, the contact 287, the arm 269, and the wires 267 and 266. Current from the source 265 also flows through the wire 264, the arm 262, the contact 279, the wires 278 and 294, and the solenoid 293, causingthe valve 257 to open, and then returns to the source 265 through the wire 292, the contact 291, the arm 26%, and the wires 267 and 266. With both valves 254 and 257 open, the excess gas in the sensor A, the tube 252, and the bellows 253 escapes through the valve 254, the tube 255, the valve 257, and the tube 260 intothe atmosphere. As a result of the decrease in pressure, the bellows 253 contracts, snapping the arm 262 of the switch 263 back from the contact 279 to the contact 280. When the arm 262 leaves the contact 279, the flow'of current to the lamp 275, the bell 276, and the solenoid 293 is broken stopping the alarm and preventing further loss of gas from the system. When the lamp 275 goes out and the bell 276 stops ringing, the switch 272 may be opened again, breaking the flow of current to the solenoid 289 and allowing the valve 254 to close. 7

If the temperature of the sensorA has not dropped below the critical value, the transducing agent B will release more gas as soon as the pressure in the sensor A has been reducedv by closing the switch 272. But, also, as soon as the pressure in the sensor A has dropped, the valve 257 closes. If the switch 272 is then opened, the pressure in the sensor A will again rise and actuate the alarm. A well-ingassed transducing agent E may be able to operate successfully after four or five cycles of giving alarm and testing for all-clear.

valve 254 to open, and then returns to the source 265 through the wire 288, the contact 285 and arm 271 of the switch 273, and the wires 267 and 266. Current also flows from the source 265 through the wire 264, the arm 262 and contact 280 of the switch 263, the wire 281, and the solenoid 282, causing the valve 256 to open, and then returns to the source 265 through the wire 283, the contact 284 and arm 270 of the switch 273, and the wires 267 and 266. Gas from the tank 259 then flows through the regulator 258, the valve 256, the tube 255, and the valve 254 into the tube 252, the bellows 253, and the sensor A. Ifthere is no leak in thesystem, the pressure in the tube 252, the bellows 253, and the sensor A builds up to the maximum valve allowed by the regulator 258, which should be set to maintain a pressure equal to that produced by exposure of the sensor A to a temperature just above the critical temperature. The resulting increase in pressure expands the bellows 253 which actuates the alarm, indicating that there is no leak in the system. In actuating the alarm, the bellows 253 causes the arm 262 of the switch 263 to snap from thecontact 284 to the contact 279, breaking the flow of current through the solenoid 282 and allowing the valve 256 to close. When the lamp 275 lights and the bell 276 rings, the test switch 273 may be opened, breaking the current flow through the solenoid 282 and allowing the valve 254 to close. After the system has been shown to have no leak, the excess gas is released to the atmosphere by closing the switch 272 as explained above, making the system ready to detect a fire.

The question arises as to whether substantial changes in the atmospheric pressure surrounding the detector might have unpredictable effects on the operation of the detector. Such pressure changes might result, for example, from operating the detector in an aircraft at high altitude. Even though the system exhausts directly into the atmosphere, the final pressure in the system depends upon the design of the bellows-actuated switch 263 and the bellows 253. As soon as the arm 262 of the switch 263 snaps from the contact 279 to the contact 280, the valve 257 closes, preventing further loss of gas, regardless of the external pressure, as long as it is not substantially higher than sea-level atmospheric pressure. Therefore, the system is not aflFected adversely by any decrease or by a slight increase in the external atmospheric pressure.

The gas in the tank 259, used to test the system for leaks, may be any convenient gas which does not cause deterioration of the equipment. However, it is preferable to use the same gas as that liberated by the transducing agent E. If a group B hydride is used as the tran'sducing agent B, then the gas in the tank 259 might This fine detector system may be tested for leaks by; V

closing the test switch 273. When the switch 273 is closed, currentfrom the source 265 flows through the wires 264 and 296 and the solenoid 289, causing the be hydrogen. Since the internal volume of the system can be made quite small, the amount of hydrogen released into the atmosphere when the valves 254, 257 are open is so small as to present no hazard, except, perhaps, under highly unusual conditions.

It should be noted that, since only the sensor A of the system extends into the fire area beyond the wall 251, no moisture, vibration, or other conditions in that area can cause the system to give a false alarm.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applicationsof the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A temperature-level detector comprising: an enclosure containing a transducing agent that releases large quantities of gas when its temperature is changed; pressure-responsive means having an interior in communication with said enclosure to make a normally closed system; manually operated normally closed bleed meansindependent of the pressure in said interior for venting said interior outside said system at any time desired during operation of the detector; and means actuated by said pressure-responsive means when the pressure in said system reaches a predetermined level.

2. The system of claim 1 having means for supplying said normally closed system with gas under pressure.

3. The system of claim 1 having means for supplying said normally closed system with gas at said predetermined level of pressure, for testing said system.

4. A temperature-level detector comprising: a tubular enclosure of. extended length containing a transducing agent that releases large quantities of gas when heated; pressure-responsive means having an interior in communication with said enclosureto make a normally closed system; manually operated valve means independent of the pressure in said enclosure and said interior for venting said interior outside said system at any time desired; and indicating means actuated by said pressure-responsive means when the pressure in said system reaches a predetermined level.

5. A temperature-level detection system comprising: a tube containing a transducing agent that releases large quantities of gas when heated; a bellows having its interior in communication with said tube; manually operated means independent of the pressure in said tube and said bellows for venting said bellows interior and tube to atmospheric pressure; means independent of the pressure in said bellows'and said tube for closing said venting means; an electrical circuit including an indicator actuated by said circuit; and a switch in said circuit actuated by movement of said bellows.

6. A temperature-level detector comprising; an elongated tube containing a transducing agent that releases largequantities of gas when heated but does not re-ingas all said gas when cooled; pressure-responsive means having an interior in communication with said enclosure to make a normally closed system; a snap-action electrical switch controlled by said pressure-responsive means for movement between first contact means and second contact means; valve means for venting said interior outside said system; and warning means actuated by movement of said switch when the pressure in said system reaches a predetermined level, and an electrical circuit including said first contact means and said warning means in series and having second switch means in parallel with said switch for energizing said valve means.

7. The system of claim 6 having means for supplying said normally closed system with gas at said predetermined level of pressure for testing said system, said means including second valve means and third switch means in said circuit for energizing said second valve means, said third switch means being energizable only when said snapaction switch engages said second contact means.

8. A temperature-level detection system comprising: a tube containing a transducing agent that releases large quantities of gas when heated; a bellows having its interior in communication with said tube; meansfor venting said bellows interior and tube to atmospheric pressure; means for closing said venting means; an electrical circuit including an indicator actuated by said circuit, the means for venting and closing being actuated by said circuit; and a switch in said circuit actuated by move ment of said bellows.

References (Jited in the file of this patent UNITED STATES PATENTS Slavin a Dec. 19, v1961 

1. A TEMPERATURE-LEVEL DETECTOR COMPRISING: AN ENCLOSURE CONTAINING A TRANSDUCING AGENT THAT RELEASES LARGE QUANTITIES OF GAS WHEN ITS TEMPERATURE IS CHANGED; PRESSURE-RESPONSIVE MEANS HAVING AN INTERIOR IN COMMUNICATION WITH SAID ENCLOSURE TO MAKE A NORMALLY CLOSED SYSTEM; MANUALLY OPERATED NORMALLY CLOSED BLEED MEANS INDEPENDENT OF THE PRESSURE IN SAID INTERIOR FOR VENTING SAID 